Surface reflectance meters of the type relating to the present invention are employed in many applications for incoming inspection and quality control. Surface reflectance meters are employed to insure that the appearance of manufactured articles are in accordance with the desired standards. For example, the paint of various body parts of an automobile may be applied at different at different times with differing batches of paint. Unless the quality of the appearance of the body parts can be measured and controlled, the differing body parts will have differing appearances which will not be pleasing to the potential buyer.
The field of the present invention relates primarily to measurements of highly reflective surfaces such as painted or polished metals or ceramics. These opaque surfaces include a predominance of specular reflection rather than diffuse reflection. The present invention is primarily applicable to measurements of distinctness of image. The distinctness of image of a reflection from a surface corresponds to the surface's ability to reflect a sharp image, which is recognizable by an observer. Distinctness of image is rated on a scale of 0 to 100, with 0 being a completely indistinct image and 100 being a completely distinct image.
It is highly desirable to have a portable meter in order to measure this quality of surface reflectance. In particular, a portable instrument which the operator can hold to the surface to be measured by hand could enable rapid incoming inspection or quality control of manufactured parts.
A difficulty exists with portable instruments which are held to the surface by hand. When using such instruments, the stability of the alignment between the instrument and the surface to be measured cannot always be assured. This is in contrast to earlier floor standing instruments which provided a much more stable alignment with the surface to be measured. In portable instruments, such as is the subject of the present invention, a momentary misalignment of the instrument with the surface to be tested can cause the surface reflectance reading to fail. In such an instance it is highly desirable to automatically detect such a reading fault and reset the surface reflectance meter to retake the measurement.